Quantitative, also called gram weight, is the most basic index of paper or cardboard, which refers to the quality of paper or cardboard per unit area, expressed in grams per square meter (g/m2). The quantitative level determines the strength of the paper or board. In general, the selection of high quantitative base paper is conducive to the improvement of the strength of corrugated cardboard and corrugated boxes, but because the corrugated cardboard production line is continuous production, the base paper must be used web, and web is sold according to quality, which means that when the quality is certain, the smaller the quantity of paper or cardboard, the larger the use area, the more products can be obtained. On the basis of ensuring strength, low-gram high-strength paper is conducive to reducing costs.
In the carton technical standards, the provisions are "surface, paper comprehensive quantitative", the quantitative unit in the Chinese and foreign standards is different, there are two quantitative expression methods: one is gram per square meter (g/m2), international general; The other is pounds per thousand square feet (lb/1000ft2), which is mainly used in the United States and Britain. The conversion relationship between the two is as follows:
1 lb/1000ft2 = 4.8824 g/m2
China's packaging paper standards are mainly divided into two parts:
1, the national standard GB/T 13024-2016 "box cardboard" (commonly known as "kraft paper"), the prescribed quantity from 90 g/m2 ~ 360 g/m2. Because China is a country with a lack of papermaking wood pulp, mainly recycled waste as raw materials, so the standard, respectively, listed "excellent products", "first-class products" and "qualified products" three, they are very different in tightness, break resistance, ring pressure, smoothness, folding resistance, water absorption and other technical indicators, and developed countries in Europe and the United States do not have the latter two, So we must pay attention to this point when we make the CAI.
2, the national standard GB/T 13023-2008 "Corrugated core (original)", the stipulated quantity from 80 g/m2 ~ 200 g/m2. But also listed "excellent products", "first-class products" and "qualified products" three, in the excellent products and subdivided "AAA", "AA" and "A" three categories, of which "excellent product AAA" physical indicators and European and American paper standards similar.
There are two national standards for quantitative determination: GB/T 451.2-2002 "Quantitative determination of paper and board" and GB/T 22811 "Quantitative determination of base paper after separation of corrugated board".
The quantitative use of the national standard GB/T 22811-2008, the corrugated board samples are impregnated to separate the constituent base paper from each other, and then the constituent base paper is dried and treated, and then the quantitative determination is carried out according to the GB/T 451.2 method of paper and cardboard.
1. Test instruments and method standards
GB/T 451.2, ISO 536, TAPPI T410
Ii. Test purpose
When we use paper, we generally use the area of the paper page, so we must ensure a certain use area, especially the reel, and increase the use area quantitatively. If the use area is guaranteed, the weight of the paper must be increased, which is bound to cause waste of raw materials. Quantitative effects on the entire physical, optical and electrical properties of the paper. General physical properties such as tensile strength, rupture resistance, tear and so on are related to quantitative. In order to compare the strength of the same type of paper with each other, it is often converted into tensile index, rupture index, tear index, etc.
Third, test principle and equipment structure
(1) Test principle
A quantitative sampler is used to accurately cut 10 samples with an area of 0.01m2, weigh them on a suitable electronic balance, and then multiply by 10 to obtain the quantitative result.
(2) Equipment structure
The external structure of the quantitative sampler (taking PN-SC100 circular quantitative sampler as an example) is shown in Figure 1.
1- Base 2- Lower knife edge 3- Upper knife edge 4- Rack 5- Handle 6- Protective cover
Figure 1 PN-SC100 circular quantitative sampler
Iv. Sample taking, processing and container preparation
The sample shall be taken according to GB/T 450, the number of samples shall not be less than five, and the total area shall be at least 10 samples. The sampling size is 100cm2(0.01m2), and the number of samples is at least 10.
In order to ensure the accuracy of sampling, the sample should be cut with a special sampler (circular quantitative sampler), and the sample area should be within the deviation range of ±1.0% in every 100 times compared with the specified area. If it is found that the cut of the sample is not up to specification, the size of each sample is accurate to 0.5mm and its area is calculated.
5. Experimental procedures and methods
Five samples were stacked vertically along the paper web into five layers, and then two stacks of 0.01m2 of samples were evenly cut along the transverse side, with a total of 10 samples. The mass m of 10 samples was accurately weighed at one time with an electronic balance with a sensitivity of 0.001g. If the mass of the sample was greater than 5g, an electronic balance with a sensitivity of 0.01g could be used to weigh the sample. Detailed quantitative test steps are shown in Figure 2. When weighing, air flow or vibration should be prevented from affecting the test accuracy of the balance.
FIG. 2 Schematic illustration of quantitative test steps
6. Result settlement analysis
Formula,
7. Possible wrong operation and error sources
(1) Cutting multiple samples at a time Cutting the thickness of 0.05mm or more paper can only be cut on a single sheet, otherwise it will reduce the service life of the instrument.
(2) The edge of the sample is not sharp, contact the manufacturer for maintenance.
(3) The phenomenon of "biting the knife" occurs
If you find the phenomenon of "gnawing knife", do not force the press, so as not to damage the cutting edge, contact the manufacturer for maintenance. (4) Only one sample is cut
Only a sample of 100cm2 is cut, weighed with a balance, and the weighing result is multiplied by 100 to obtain a quantitative value. This deviation is relatively large, not representative.
(5) Electronic balance accuracy is not enough
According to the standard requirements, the quantity value should be accurate to 0.001g, and in theory, it is enough to use a balance with a sensitivity of 0.001g. However, in the actual work, it is very likely to encounter the end of the balance drift, can not guarantee the accuracy. In order to ensure accuracy, it is best to choose an electronic balance with a sensitivity of 0.0001g. The weighing results are accurate to three decimal places.
(6) After each weighing, the indicating value does not return to zero
The balance is not levelled, not preheated, not preloaded, poor linearity and not calibrated after changing position may result in this situation where the indicator value does not return to zero. The electronic balance is an electronic instrument, which should be preheated for more than 30min before measurement, so that the internal electronic devices can achieve a thermal stable balance. Preloading is a short pressure and pressure relief operation on the electronic balance, because after the balance is not used for a long time, its internal sensor is in a dormant state, and the metal shrapnel also stops working, and the performance of the electronic balance is in an unstable state, indicating stability and return to zero are not good. Before the electronic balance is used for the first time, the level is adjusted first, the power is preheated, the measurement is preloaded first, and the calibration is carried out regularly.
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This paper was published in Carton World magazine in March 2023
